The analysis of a water, e.g. waste water or surface water, for phenols is important in determining the quality of the water. The "total phenol" content of the water is often determined by the standard 4-aminoantipyrene colorimetric method as outlined in Standard Methods For The Examination Of Water And Wastewater, published jointly by the American Public Health Association, the American Water Works Association and the Water Pollution Control Federation. Individual phenols, such as 2,4,6-trichlorophenol are typically determined by gas or liquid chromatography.
Derivatization is a commonly used sample pretreatment step to enhance the chromatographic characteristics or the detectability of a sample component of interest. For example, many phenols can be derivatized with diazomethane to form a methyl ether of the parent phenol for gas chromatographic analysis and derivatization with 5-dimethylamino-1-naphthaline sulfonyl chloride has been done for fluorescence detection liquid chromatography. The Handbook of Analytical Derivatization Reactions authored by Daniel R. Knapp and published by John Wiley & Sons is one source of information regarding derivatization reactions for chromatography.
Phenols have also been titrated by reaction with an excess of bromine produced by the bromate-bromide reaction to brominate the phenol and then a back titration to determine the amount of bromine consumed by the bromination. Different phenols consume different amounts of bromine. For example, phenol, salicylic acid, acetylsalicylic acid, m-cresol, sulfamic acid and m-toluidine consume three moles of Br.sub.2 per mole of the phenol (to produce a tribrominated moiety) while beta-naphthol consumes only one mole of Br.sub.2. More information on the titration of phenols with bromine can be had by reference to Fundamentals of Analytical Chemistry authored by Skoog and West and published by Holt, Rinehart and Winston. Phenols are not generally bromination titrated in samples of surface water because in such water the concentration of phenols is almost always below the reliable detection limit of the method.
Backflow liquid chromatography is a known technique wherein a sample is injected into the inlet end of a liquid chromatographic column and developed by a flow of the liquid mobile phase directed into the inlet end of the column until the earliest to elute component of interest of the sample is just about to elute from the outlet end of the column. Then, the flow of mobile phase is reversed through the column so that the sample components in the column "roll up" toward the inlet end of the column and tend to elute from the inlet end of the column as a single chromatographic band. By this technique, sample components that elute from the outlet end of the column before the earliest to elute component of interest nears the outlet end of the column are discarded and do not become part of the single chromatographic band mentioned above.
Membrane assisted chromatography is a known technique wherein a membrane is used to partition a sample containing a component of interest from an extractant. The component of interest permeates across the membrane into the extractant which is then subjected to a chromatographic determination. The specific membrane and extractant used are selected to enhance the permeation of the sample component of interest and to minimize or eliminate the permeation of other components of the sample that may interfere with the chromatographic determination of the component of interest. U.S. Pat. No. 4,775,476 to Richard G. Melcher and Hernan J. Cortes is an example of membrane assisted liquid chromatography.
The "total phenol" 4-aminoantipyrene colorimetric method does not determine individual phenols. However, it can be important to determine the individual phenols that make up the "total phenols" and it should be noted that not all phenols respond or respond equally in the 4-aminoantipyerene colorimetric method. High Performance Liquid Chromatography (HPLC) with an ultraviolet detector or an electrochemical detector can be used to determine the individual phenols but several problems can occur. First, the different phenols, e.g., phenol and 2,4,6-trichlorophenol, can have different spectrophotometric molar absorptivities at the detection wavelength, different maximum absorption wavelengths and, for the electrochemical detector, different electrochemical reaction characteristics. Second, the different phenols, e.g., phenol and 2,4,6-trichlorophenol, can have significantly different chromatographic characteristics. In reverse phase HPLC, phenol tends to elute early in the chromatogram with other interfering non-phenol components of the sample.
Frei et al., Chemical Derivatization in Analytical Chemistry, Chromatography, 1, 53-54, (1981), published by Plenum Press, pointed to a possible solution to these problems, i.e., treat a sample of water with bromine to brominate any phenols in the water, extract the brominated phenols from the water and then chromatograph the extracted brominated phenols. Jandera et al., Gradient Elution In Column Liquid Chromatography Theory And Practice, 298, (1985), published by Elsevier, suggests that halogenated phenols tend to elute later in a reverse phase chromatogram than their parent non-halogenated phenols and many liquid chromatographers know this as general knowledge from experience. However, when the present inventors tried the approach pointed to in Frei et al., it was discovered that the brominated phenols were apparently being partially destroyed by the remaining bromine during the bromination process, probably by a mechanism analogous to superchlorination. This destruction problem could be controlled by reducing the bromine concentration during the bromination step and by reducing the time of the bromination step but then the procedure was not applicable for samples that contained enough phenols and other components to substantially use up all of the bromine added during the bromination step before all of the phenols were completely brominated. A bromination derivatization chromatographic method is needed for the determination of phenols in water that solves this problem.